The present invention relates generally to seals between rotatary and stationary components of a steam turbine and more particularly to a seal activated by a pressure differential formed across the rotary component and the stationary component of a steam turbine.
In a steam turbine, a seal between rotary and stationary components is an important part of the steam turbine performance. It will be appreciated that the greater the number and magnitude of steam leakage paths, the greater the losses of efficiency of the steam turbine. For example, labyrinth seal teeth often used to seal between the diaphragms of the stationary component and the rotor or between the rotor bucket tips and the stationary shroud of the rotary component require substantial clearances to be maintained to allow for radial and circumferential movement during transient operations such as startup and shutdown of the steam turbine. These clearances are, of course, detrimental to sealing. There are also clearance issues associated with multiple independent seal surfaces, tolerance stack up of radial clearances and assembly of multiple seals, all of which can diminish steam turbine efficiency. Moreover, it is often difficult to create seals which not only increase the efficiency of the steam turbine but also increase the ability to service and repair various parts of the turbine as well as to create known repeatable boundary conditions for such parts.